*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
.box{
    width: 1200px;
    height: 840px;
    position: absolute;
    background-color: white;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    margin: auto;
}
.son{
    display: none;
    width: 400px;
    height: 300px;
    background-color: pink;
    position: absolute;
    margin-top: 500px;
    margin-left: 500px;
}
.yhm{
    margin-top: 20px;
}
.nl{
    margin-top: 20px;
}
.a1{
    margin-top: 20px;
}
table{
    margin-left: 250px;
    margin-top: 5px;
    border-spacing: 0;
}
th,td{
    width: 220px;
    height: 42px;
}